Autoamtic hoist control



p 1951 D. WERTMAN ET AL 5 3 AUTOMATIC HOIST CONTROL Filed Sept. 29, 1950 INVENTORS DAV/D WERTMA/V ROBERT KBOLE ATTORNEYS Patented Sept. 4, 1951 AUTOMATIC HOISTGONTROL David Wert-man,M ount Rainier, and Robert K. -Bo'le, Bethesda, Md.

Application September 29, 1950., Serial .No. 187,651 '9Claims. (01.19-8-221') (Granted nnderthe act of March 3, 18.83, as

amended April 30, 1928; 37-0 0. G. 757) Heretofore, equipment iormaising 'or lowering I articlesirom one station *to another has usually been of the endless chain conveyor typain which an endless chain passes through a, hoist tube-and over sprockets at the'ends'of-thehoist, the chain being provided with uniformly spaced .flightsfior carrying the articles being raised .101 lowered. The conveyor usualiymoves in stagesito give the handlers opportunity to place objects on each flight as it reaches the loading station and to remove objects from each'flight as it reaches the unloading station. A housing .and hoist'tube of a size to accommodate the chain, flights, and sprocket wheels require a large aamountiof space that could be otherwise used, ascfor thersto'rage of the articles to-be handled; particularlyis this so when such hoists are used for serving ammiinition to guns aboard fightingships. Furthermore, in hoists of this o1ass, the lengthof'chain and the number of Lfiightsrec uired must be at least double what is actually utilized 'formovin objects during a single cycle, and thus large masses which are not immediately concerned with object movement must bepreoisely controlled during operation of the-hoist. Brakesor the like need be provided in the abovesmentioned endless chain type hoist to retain it at the-desired position between flight advancements, since the weight of all articles "carried thereon tend to move the hoist downwardly. Hence, to properly control conveyors or hoists oi'this general :class complicated hydro-mechanical mechanismshave heretofore been employed and, for completely automatic operation, the equipment-required has been prodigioua-subjectmg the hoist to frequent breakdown and render'mgthe task of diagnosing casualties exceedingly complex.

The present invention contemplates providing a hydraulic conveyor or hoist of the bar type particularly adapted for vertical conveying of objects either up or down by stepwise'increments through vertical reciprocation of the hoist'bar. This bar is provided with-a plurality of spaced pawls which engage objects to move them within a suitable hoist tube one flight for eachbar-reciprocation, the objects resting at-each'suecess-ive flight stage on tube pawls stationary with respect to bar reciprocation, so that the reciprocatory conveying movement of the bar needbe only slightlygreater thanthe distance between two successive tube pawls, or the distance of one flight. A'hydraulic control unit is provided havingaplurality of valves whose operation is correlated with the load condition and hoist position, through suitable mechanical linkage therebetweenior automatically initiating object conveying movement oithe hoist bar only whenan operativeload condition exists in the hoist tube and 'forautomatically reversing and stopping the movement of the'hoist'ba-r at thexproper points in its cyc'le. Means are provided for manually controlling 'the'hoist'in the event of valve breakdown or during drills.

. An object, therefore, of the present invention is to provide an automatic control system for a hoist or conveyor tfunctioning to initiate object conveying operations only when a certain load condition exists on said hoist.

Anotherobj-ect of theinvention is to provide an automatic-control system for a stepwise hoist or conveyor oi the type indicated which is responsive to the hoist or conveyor load in initiatlug conveyor operation and thereafter being responsiveto the movement of said hoist or conveyor in controlling the operation thereof.

Another object of the invention is to provide areci-procating'hoist Or conveyor to move objects through a succession of steps 01' flights wherein the hoist or conveyorrec-iprocates over a distance substantially equalto the distance between two successive steps or flights.

Another object of the invention is to provide a hoist or conveyor which reciprocates between two positions for conveying objects by stepwise advancemen-t in-either of two directions as desired.

Another object of the invention isto provide'a hoist-or conveyor for moving objects between a loading and unloading station and a control systemtherefor responsive to the load condition existent on said hoist or conveyor, making the hoist or conveyor operative only when the loading station is-charged and the unloading station is discharged.

Another object of the invention is to provide a conveyor and control system therefor, said control system determining the direction of conveyor load movement, said control system being responsive to the load condition on the conveyor to permit operation of the conveyor only under a desired'load condition, and said-control system being responsive to conveyor movement for controlling its operation.

Other objects and, their atten'dant advantages willzbecome'apparent-as the following detailed as the tilting plate designated by the numeral Motor I I) has a second output shaft Ila l3. which drives through any suitable gear arrangement a servo pump I4 and a control pump I5,

both of which are preferably of the positiverdisplacement type. The function of these latter two pumps will be later described. i

4 that is above the piston is forced back toward the pump through a conduit and passageway 32. Since the piston rod I9a occupies a certain portion of the space in the hydraulic cylinder 28, the fluid that is forced out of the cylinder does not'supply the pump with a sufficient quantity to complete theupstroke of the piston H). The excess fluid required is therefore supplied through the check valve 25a which admits the proper quantity from passage 25 to passage 32.

As the piston I9 approaches the top of the stroke, an upper-buffing piston 33 on the top ,of the piston enters an upper buffing chamber 34 and decelerates the piston and hoist bar.

Leakage between the piston 33 and the sides of the buffing chamber 34 permits the piston I9 Hydraulic pump I2 is supplied with operating I fluid, such as oil, from a suitable expansion tank IT by conduit I6 which leads to certain ports or passages in a hydraulic piston control block I8. The purpose of the hydraulic pump I2 is to provide fluid pressure to the appropriate side of a double acting piston I9 which operates in a cylinder 28 to raiseor lower a hoist bar,:indicated generally by the numeral which may operate in a conventional hoist tube (not shown). The hoist bar 20 is provided with pawls 2| which engage the objects, such as the projectiles 22, that are to be raised or lowered and move them between loading and unloading stations through a succession of flights or increments one flight at a time, the objects being retained at each flight by tube pawls 23. has moved sufiiciently to insure proper seating of the objects (hereinafter referred to as projectiles for purposes of illustration though it must be understood that the hoist is adaptable for raising or lowering other types of objects) on the proper tube pawls 23 its direction of movement is reversed so that on the next movement of the bar in the object advancing direction a projectile is moved one more flight by the hoist bar pawl 2I next above or below the one which last engaged the projectile according to whether the projectile is being raised or lowered.

In order, therefore, to reciprocate the-rack bar 20, it is necessary to direct the fluid flow alternately to the opposite sides of the piston I9. The supply fluid enters the hydraulic piston control block Hi from conduit I6 through inlet passage 25 which is communicated through the check valves 25a and 251) with the pump I2. All passages, chambers, and the likecommunicating with passage 25 are completely filled with fluid, but it should be understood that with the parts of the hoist in the position shown thisfluid-is not under operating pressure. When the piston I9 is to be raised the tilting plate I3 is; moved from the position illustrated, which is the neutral position, to the left toward the stop 24, either manually by means of a lever I3a. or automatically by means to be later described. This movement of the tilting plate causes the pump to discharge oil through a lower passage 26 in block I8 to the chamber of an emergency stop valve 21 from which it flows via passageway and conduit 26a to the lower side of the piston I9. Fluid is also ported from conduit 26a-through a lower check valve 260 to a lower bufling chamber 30, which is shown occupied by a buffing piston 3| on the bottom of the piston l9.

As the piston is driven upwardly by the pressure of the fluid acting on its bottom, the fluid When the hoist barto complete its stroke.

When the piston has reached the top of its stroke and before it has started to descend, pressure for a limited periodis exerted on the bottom thereof by the continued pumping action of the pump I2. To prevent excessive pressure from building up. a relief valve 35 is provided communicating passage 26 with passage 32 so that the unused fluid may readily recirculate through the pump I2 without damage to any of the parts.

After the projectiles 22 are in position to be seated on the tube pawls 23 as aforesaid and other operations tobe described have been performed, the hoist bar 20 and piston I9 are ready to descend. To reverse the flow of fluid to the cylinder 28 the tilting plate I3 is moved from its left position toward'the right stop 23. This may be done as before either manually by lever I3a or automatically, so that the pump l2 may now discharge oil through passage 32 to the top of the piston I9. Fluid also passes through an upper check .valve 132a and enters the upper bufiing chamber 34 in readiness for the next succeeding upstroke.

The fluid beneath'the piston I9 is ported to the pump via passage 26a, the chamber of the emergency stop valve 21, and passage 25. As the piston approaches'the bottom of the stroke, lower bufier piston 3| thereof enters the buffing chamber 30 and decelerates the piston as has already been described for the upstroke. Because of the space occupied by piston rod l9a, less fluid can be received above the piston I9 than is forced out from below. This excess fiuid is discharged through a second relief valve 36 to a conduit 31 leading back to the expansion tank I! as illustrated.-

In the event that the hoist must be halted at any point in its operation, the emergency stop valve 21 is provided which is normally urged by a spring 40 toward the up or closed position. However, a solenoid Me, which may be connected in one phase of the motor power supply, during normal operation holds the emergency valve 2'! open. Inorder to stop the'hoist a button (not shown) may be pushed to'stop the motor I0 and permit the valve 21 to close quickly so that land 4| thereof can instantly shut off the flow of fluid through the passage 26. If the piston is on its upstroke the weight of the bar and the resistance of the fluid above the piston will decelerate and stop these members almost instantaneously. should the piston, however, be on the down stroke excessive pressure is likely to occur. To avoid this upper land 42 of valve 21 uncovers a passageway 43- so that passage 26a will be in communication with return conduit 31 through a relief valve 43a, which is set to open only when assess:

ginagzhuum pressure obtains beneath the pie 'on l 7 As has been hercinbefore mentioned, motor Ii) drives a control pumpliand a servo pump M which receive iiuid from tank 11 through a branch line 1 5a. This fluid is pumpedthrough suitable filters 15a andlia, and lines 151) and Nb respectively to certain portsand passages in a control valve block, indlcated generally"by the numeraltfl. The pumps 1 Sand l4 may have substantially similar characteristics and it is to be understood that they create a constant positive headin thelines 5b and Hi) at all times durin the operation of the hoist.

Fromlines 15b and 14b fluid-flows to chambers of a function-"controlvalve 5i whenceit passes into passagewaysinthe control valve'hlockill.

' The function control valve is operated by a hand lever 52' which is illustratedin' the raise position. When the lever 52 i-s moved tothe lower position the function control valveil covers and uncovers other ports and passageways so that the hoist operates'to lower the projectiles.

Referring now to the right-hand portion'oi' the drawing and particularly to the system of linkages there illustrated, therewillbeohserved a lowerbell crank '58 whichhas afixed pivot '51. The end of the-short arm 5311' of the boil-crank is arcuate as shown-and the long arm53h is urged in a "counterclockwisedirection'by means of a spn'ng loaded rod $26 which operates through anaperture in'a "fixed portion-56a. Thearrangement issuch that when aprojectileisplaced on the loading platform 57 of the hoist tube, the

side of the projectile "pushes against the arcuate portion of the arm '53a't-o pivot thebell crank 53 clockwise and force the rod 55 downwardly against its spring. Pivotally 'attached'to the end "of the arm 53b is an elongated link 55 whic ris pivotally' secured at'its upper end to one end of a couple link 58 which in turn ispivotally-attached at its center to one "arm of a small'bell crank '59 having a fixed pivot 59a. Attached to the opposite end of couple link Ellis the lower end of a link 60 which is pivotally" secured at its upper end to an elongated arm 'filaoian' upper bell crank'lii which is pivoted 'att'd' andurged clockwise by the'spring loadedrodfiz operating through a fixed portion'oza. 'Thearrangement is such that when a projectile contacts thearcuate end of the short arm 'Elb, the bell crank 6| will be rotated counterclockwise against the rod 62 forcing it upwardly against the pressure of its spring.

To the upper arm of the aforesaid small bell crank 59 there is pivotallysecured one end of an elongated horizontalrod 65 whose opposite end extends through the wall of housing member 5911 and is'pivotally secured to a pivot arm 68 which is mounted on a suitable bracket 66a attached to the side of the control valve block 58. The length of arm 66 is substantially equal to the length of the upper arm of the bell crank 59 so that movement of the latter will impart motion through link 65 and armBBto a valve stem 61a of a valve 51 disposed in the top of'the control valve block 50. It should be noted that valve 61 is provided at its left end with a spring Sin which normally acts between shoulders to move and to retain said valve in the position illustrated, which is the neutral position.

The valve 6? is an interlock valve, the operation of which will become readily apparent'as the description proceeds, and its function is to initiate the conveying operations according to the load 6 condition. For example, with vthe two projec tiles "22 seated on the tube pawls 23 at the two intermediate flights as illustrated in the drawing, when a projectile is put on the loading platform 57 the lower bell crank 53 is rotated cl0ckwise causing couple link 58 to rotate counterclockwise about the end of link which is restrained from upward'movement by the spring loaded rod 62. Hence couple link 58 acts'as a lever with the lower arm of small bell crank59 pivoted midway of its length. It will be apparent,

theretore, thatzbell crank '59 will pivot clockwise andthus draw-valve 61 toward the right position, shown in dotted lines, to initiate a hoisting operation.

When the lowestprojectile has cleared the arm 53a of'lower bell crank 53, all the parts of the linkage arrangement will be returned through the action of the spring loaded rod 515 and interlock valve spring fiib to the positions showniin-the drawings. However, as the hoist continues .to ascend, the uppermost projectile engages the arm Gib of the upper interlock bell crank SI and cams-it in a counterclockwise direction so that now the couple link'tfl will pivot as a lever counterclockwise about. the end of link 55. This causes 'smallbell crank 58 torotate counterclockwise so thatthe'valve'fi'l moves to the left to the position' also shown in'dottsd lines. This same effect is achieved when a: projectile is placed in the top of the hoist tube duringlowering operation and,

as will become apparent, in the latter instance a lowering cycle is initiated. When the upper projecticle is moved out of contact with the upper bell crank 36 I the: interlock valve and the'above described linkage assume the position shown the drawing and no further projectile moving operations my be performed until" the interiockvalve El is'moved one way or the other "by a projeotileacting on either the upper or lower interlock'bell crank 15! and 53 in a-mamrorsuh 'stantially as described.

When projectiies are in thetop and'bottom positions of the hoist tube=at the same timethe ti'on, and thebar- Zilis not actuated. Thus a pro- 'jectile cannot -'be raised against the base of one 'inthe'uppermcst position'before it has-been re moved from the hoist tuhe;"nor can a projectile be lowered on the nose of one seated on lower platformtl. If desired the interlockvalve may also b'e operated in a similar manner and in combination-with the shown linkage by the. conven- 'tionalshutters (notshown) which arenormally provided at the top andbott'om of a projectile hoist. Thus, when either shutteris open-the arrangement of linkages connected therewith may operate to place the interlock valve in such a position that operation of the hoist cannot beresumed until the shutters have been properly closed. v

"Referring now to the valve control block '51! and particularly to servo inlet passage l lb, with'the function control valve 5! in the "raise position fluid passes from a chamber'thercof'through two vertically spacedpassageways lilo and'idb. The passage 'w'badinits fluid to the interlock valvejii'l where further passageis blocked by a land there of. Passage l la'admits fluid to a chamber of "a reversing valve '13 from which fluid flows via a "passage 'lilc'through a chamberin a bottom-ofwhich operates in a control block 80 and has pivoted medianly thereto the upper end of the tilting plate I3. Fluid is also ported from conduit 10d through an orifice 83a to a chamber of a right neutral positioning piston 83 having an extension 831) which extends horizontally through a suitable aperture in the tilting plate control block 80 to abut the right end of tilting platepositioning piston 82 when the parts of the hoist are in the position shown.

Located above the reversing valve 13 and branching to the left and right from the passage 10a is a horizontal passage 19) from the right branch of which at 70a fluid flows through a chamber of the reversing valve 13 and a passage 10k to a chamber in. the bottom-of-stroke valve 12 and passes to a conduit 199 leading to the lefthand end of the tilting plate positioning piston 82. Fluid is also ported from conduit 10g through an orifice 84a to a chamber of a left neutral positioning piston 54 which is provided with an eX- tension 84b and is similar in all respects to the piston 83 already described.

It will now be apparent that with all of the parts of the hoist in the position illustrated fluid flows equally to both sides of the tilting plate positioning piston 82 and the tilting plate will be thus retained in its neutral position so that no fluid may be discharged by pump l2 to either side of piston I9. Since servo fluid cannot otherwise escape from the system a relief valve 85 is provided in the left end of the horizontal passage '15) to vent excess fluid to a drain passage l'la leadin: back to the expansion tank H.

With the function control valve in the position of "raise and with no projectile in the top flight of the hoist so that upper interlock bell crank 61 is not retracted, when a projectile is placed on the loading platform 51 the lower interlock bell crank 53 will be rotated to move the interlock valve 61 to its right position asalready described. This ports the aforesaid passage 1% to a chamber 610 of the interlock valve which communicates the former with a passage 11 so that fluid may flow downwardly through the control block 50 to the right-hand chamber of the bottom-of-stroke valve 1-2 whence it passes upwardly through a passage Ha to the right-hand end of the reversing valve [3. This end of the reversing valve is provided with horizontally spaced annular grooves with which nonpositive detents 13c engage so that the reversing valve 13 may be releasably retained in the right position shown or in the left position to which it will be forced by the admission of the fluid to its right end. When the reversing valve 13 has been moved to the left the passages [00 and k will be closed to communication with passages 10a and "if. However, a passage 10h will be uncovered by the reversing valve 13 and servo fluid continues to flow through passage 10a to conduit Ind and the right hand end of the tilting plate positioning piston 82. Conduit 109, leading to the left end of the tilting plate positioning piston, is now communicated by way of a passage 19 with a return passage 90 in communication with drain passage "a leading to the expansion tank l1.

Since pressure is now exerted only on the right end of the tilting plate positioning piston, and the left hand end of this member is vented to the expansion tank, the tilting plate positioning piston 82 -is moved to the left causing the tilting plate H to approach the stop 24. The orifice 84a limits the speed of fluid escape from the chamber of the left neutral positioning piston 8 4 thereby controlling the acceleration of the hoist bar 29 to within desired limits. Oriflces 83a for the right neutral positioning piston 83 serves in a similar manner to control the rate of acceleration of the hoist bar when starting its down stroke.

Referring now to hoist bar 20 and particularly to the pawls 2| thereon it will be observed that they are pivotally mounted in slotted members 21a and are of the shape shown so that when the hoist descends during the down stroke of a raising cycle the pawls may be pushed aside'by vertical sides of projectile on lower flights so that the downward movement of the barwill not be obstructed. When the bar has descended sufilciently so that each pawl is beneath the projectile it is to engage on the next ascent, gravity or light springs (not shown) rotate the pawls clockwise to projectile engaging position, suitable stops (not shown), of course, being provided to retain the pawls in this position.

On the lower two slotted members 21a are projecting bosses Nb and 2 [0. The purpose of these bosses is to engage a lever arm 9| which is pivotally supported by bracket 9 la secured to the side of the control valve block 50. Attached to the shaft and operated by the lever'9i in fixed-angu lar relationship therewith are two arms 92 and 93. The arrangement is such that when piston I 9 approaches the bottom of its stroke, the upper boss Zlb on the hoist bar engages lever 9|, causing the end of arm 92 to contact the horizontally projecting stem of the bottom-o-f-stroke valve 12 and force it to the left against the pressure of a spring 12b. In a like manner, when the piston l9 approaches the top of its stroke, the lower boss" 2: engages lever 9| moving it counterclockwise so that end of upper arm 93 contacts the horizontally projecting stem of a top-of-stroke valve 80, and urges it to the left against the pressure of a spring 802). It will be noted that intermediately disposed on the arm 93 is a rod 9312 whose function is to contact the projecting stem of a tube pawl control valve 95 to be hereinafter described. Valve 95 is movable between the position shown and a right extended position indicated by the dotted lines. With valve 95 in the position shown, a spring about rod 93a allows a certain amount of lost motion thereof to permit lever 93 to continue moving after valve 95 has been contacted by rod 93a so that valve may be thereafter shifted to the left as above-described. 1

Immediately, therefore, after a projectile has been placed on the lower platform 5'! of the hoist tube and the reversing valve 13 has been moved I to the left so thatfluid is delivered by pump l2 the underside of piston I9, all as above-described, the boss Zlb on the hoist bar 20 releases lever 9| sothat spring 12b of bottom-of-stroke valve 12 may move it to the right to block the fluid flowing through passag Ha to the right end of the reversing valve 13 which nevertheless, remains in its left posit-ion because of the aforesaid nonpositive detents 130. With the bottom-of-stroke valve 12 in itsright position, passage H a is vented to the expansion tank I! through a horizontal passage I'lc communicating with drain passage Ila. As piston 19 ascends, the projectiles 22 on the tube pawls 23 are engaged by the hoist pawls 2| to be lifted one flight as described. When the lowest projectile moves out of contact with bell "crank 53 the interlock valve 61 moves to the neu- .aeeasoi corresponding tube pawl the top-of-stroke valve '80 is forced by end of arm 93 to the left against "the pressure of itsspring 80b; A horizontal ex.- tension 80c secured to the-left endof the-top-ofs stroke valve 8.0 abuts the right. endofa valve [B, hereinafter referredto as a latohvalve, .and also moves it to the left against the pressure of. its spring 100a. The function of the latchvalve will be later described;

With the top-of-stroke valve 80in the leftlposition, a horizontal passageway Hip, branching from passage llia, is communicated with a passage 101' which admits fluid to the. left end-10f. th'e 'reversing valve 13 forcing it. to the right to. the

position illustrated where it is retained by the nonpositive detent 13c. Itmust be remembered that bottom-of-stroke valve 'T2.has already been moved to it right hand position lay-.itsspring-lZ-b. Hence, when the reversingvalve.l3.is'.moved:to the right, passageway 'i'fld will be communicated through a chamber in the bottom-ofestroke valve 12 and a passage. isiwith a chamberofathe re.- versing valve 73 from which fluid. may. flow through aforesaid passage 90 toreturn passage flu and thus .be discharged to the expansion tank I1. Furthermore, when thebottom-ofs-stroke valve 42 is in its rightmost positionservo fluid at the extreme right end of; the h0riz'ontal passage "mi is now communicated through the reversing valve 73, a passage m, and. a chamber-of the bottom-of-stroke valve, witheonduit Tilgleading to the left end of the tilting plate positioning piston 82 to urge the plate towardthe right'stop 23. This reverses the hydraulic pump l2 asexplained so that the piston lfl. starts is descent. After about the first inch of downward movement of the hoist; lower boss 21c thereon releases lever -9| so that top-of-stroke valve 80 and latch valve its left position. As the hoist bar descends and before it has reached its maximum velocity the projectiles are depositedjon their correspondin tube p w s so that the hoist completes; the re- -mainder of its down stroke in an unloadedcondition. i

As the hoist nears the bottomof its stroke the,

bottom-of-stroke valve 12 isforcedto the-. left so thatall of the valves .of the hoistassumethe position depicted in the illustration'and ffiui'd thus flows equally to both sides of thejtiltingplate positioning piston 82. Since therighthandend of the tilting plate positioning piston .is inabu't ment with the extension 83b of the right neutral positioning piston 83, a differential area is pro.-

vided by the latter against which the.flui'd may act to move piston 83 and piston 82"to the left until the left end of the latter contacts extension 8412 of th left neutral positioningpistonfifi. The forces acting on both sides of a tilting plate positioning piston-82 will now bebalanced-sothatthis '-member will be retained inthe neutral position of the drawing resulting in a cessation of :pumping'action-by thepump 1 2.

It should be understood thatrthei hoist .as Edescribed to this point, has been primarily depicted .as it would be employed to :raise sproiefitiles. When it is desired .to lower projectiles, it will be 'obvious that the hoist 20 must first ascend toward its uppermost position before th hoist pawls 2| engage any projectiles in the hoist tube. In order to accomplish this, therefore, means must be provided to move the hoist pawls 2! clear of projectiles immediately above these pawls as the hoist ascends and furthermore, means must be provided to retract the tube pawls 23 clear of descending projectiles until each has been moved to the next lower flight at which point the tube pawlsmust assume a-projectile retaining position.v The tube pawls must remain in this positionuntil on the next upstroke the proper hoist pawls have lifted the projectiles from their corresponding tube pawls whereupon they must again be retracted clear of all projectiles so that the latter may be lowered an additional flight.

With reference to the right side of the drawing the means for actuating the tube pawls in correlation with hoist bar position comprises a bar 'lfi'l mounted atop a double acting piston Hi3 dis,- posed in a cylinder 194 which receives fluid in proper sequence to its-top or bottom by means of upper and lower. conduits Hi5 and Hit respectively. The bar H)? has equally spaced thereon suitable slotted portions 230 in which are pivotally secured the ends of link arms 23a whose oppositeends are pivoted to fixed portions 231) of the hoist tube. The tube pawls 23 are also pivoted to the fixed portions 231) and are so arranged that they may be moved clockwise relative to link arm. 23aby ascending projectiles during the upstroke phase of a raising cycle. However, when the loaded hoist bar is on the down stroke phase of'alowering cycle the tube pawls 2-3 are retracted 'in a clockwise direction by the link arms when they are moved downwardly by the admission of fluid. to the top of cylinder H34 in proper timed relationship with hoist bar position.

'Referring' to the hoist bar, 29 .i hepawls 2| thereof are provided with toes. 31d- WhiQh DI ject slightly to the left of the slotted members 21a as illustrated. An. elongated vertical rod i913,

*mounted atop a double acting piston Hi9 operat- --ing 'in'a cylinder Hi1, has'thereon p irs of spac 'co'llars 188b, the lower collar of each pair being "fixed to the rod we and the upper collar being --'.slidable thereon and spring urged downwardly as --il-lustrated.- Between the-adia es of ch pair of collarsthere. are dispo$ed the rounded b --furcated ends of arms of tripping cams I 030 which are pivoted to. fixed portions 560. The tripping .camsextend into the path of the toes 2 Id of the bar pawls 21 when the piston m9 is moved down.- wardly by the admission of fluid to the upper end lofthexcylinder- I H]. The tripping cams are extended throu hout the entire lowering cycle and :are contacted byv 1 h? toes lid on both the up and xdQWIl stroke. of the hoist bar- Onthe upstroke, the hoist pawls engage the tripping cams lilac and are-rotated wcounterelockwiseclear of projectiles i mediately above them. When thehoist bar -p awls- 2-]; havepassed above the projectiles thus :avoided they return to their normal position. The toes on the pawls 2| are arranged so that they do potengagethe tripping cams at the top of the .stroke. On the down stroke of the loaded hoist bar, the.toes 21d again contact the tripping cams ,liiBc which are rotated clockwise against the springs of the upper slidable collars on the rod 108 and thus do not .obstruct the hoist bar.

, ihe. tripping cam operating piston 19 and the ;-tub,e pawl control piston [M are actuated by Control fluid delivered .by the control pump i5). With ,the. lever 52 in the position of raise, control fluid from conduit I5b enters the control valve block 50 to the appropriate chamber of the function control valve 5| whence it is ported to conduit I20 leading to the bottom of the cylinder I I urging piston I09 in the upper position shown where it remains throughout all phases of projectile raising cycles. A branch passage I20a depending from conduit I 20 admits fluid to the bottom of a piston I I operating in the tilting plate control block 80 as illustrated. Piston -I I5, which will b hereinafter referred to as a stroke limit piston and later described in detail, is also re- 'iained in the up position throughout projectile raising operations. Additional controlfluid is ported from the function control valve 5| to a passageway I22 which conducts fluid to the right hand end of a tube pawl control valve 95 so that this member will be urged to its left position throughout the projectile raising cycle. With the tube pawl control valve 95 in this position fluid is now communicated through the left chamber thereof with the conduit I06 leading to the lower end of the tube pawl control cylinder I04 urging piston I09 upwardly where it also is retained throughout the entire projectile raising cycle.

Fluid not required for retaining these three pistons in their upper position escapes through an orifice Ib, located near the upper left hand corner of the control block 50, to the drain passage I'Ia and returns there through to the expansion tank IL Orifice I20b further serves to maintain a back pressure in the control circuit to insure retention of all pistons in their upper position. The tube pawl control rod I01, the hoist pawl control rod I08, and the stroke limit piston H5 are provided with springs I0'Ia, I08d, and II5a respectively which also urge each of the aforesaid members to their upper position shown in the drawing.

When lever 52 is moved downwardly to flower" position the tripping cam operating cylinder H0 'and the stroke limit piston II5 are moved immediately to their down position where they remain throughout projectile lowering cycle. This occurs when the function control valve uncovers a conduit I2I which admits fluid to the upper end of tripping cam control cylinder III) 5 and to a branch passage I2Ia leading to the *upper end of the stroke limit piston II5. Furthermore, with the function control valve in the 'lower position, a chamber thereof communicates conduit I20 with the drain passage IIa so that as the pistons I09 and H5 are moved fdownwa'rdly the fluid therebeneath will be' returned to the expansion tank I1. Additional .1 control fluid is conducted through a chamber of the function control valve to a passage I leading to a chamber of a differential piston 95a on the left end of the tube pawl control valve '95. Fluid which had previously been acting on the right-hand end of tube pawl control valve F95 as above explained is vented to the expansion tank through passage I22 which is now communicated with drain passage I'Ia. through the function control valve.

Control fluid acting on the differential piston 95a moves the tube pawl control valve 95 to its extreme right position to communicate passage I25 with passage I06 leading to the bottom of they tube pawl control piston I03 so that it continues .to remain in the upper position. As the hoist bar 20 moves upwardly and approaches-the top of its stroke, rod 93a on the upper hoist-operated arm 93 contacts the rightwardly extending stem of the tube pawl control valve 95 and forces expansion tank I1.

fluid acting on the piston 95a. The spring force on rod-93a is greater than the hydraulic force on piston 950, so that the lost motion of rod 93a does not. come into play until valve 95 has been moved completely to the left. The central small land of valve 95 shuts off control fluid from passage I25tc conduit I06 leading to the bottom of tube pawl control cylinder I04 and the latter passage'is vented to passage I22 which, it will be remembered, is in communication with the .At the same time passage I25 is communicated through the right chamber of the tube pawl control valve with a passage I26 leadingfto the latch valve I00 which is still in the right extended position of the illustration so that further passage of the fluid is temporarily blocked. As the hoist bar 20 continues its ascent and after all projectiles have. been lifted from their tube pawls, the end of arm .93 contacts the stem of top-of-stroke valve and moves it and the latch valve I00 to the left against the pressure of their springs 80b and mm: respectively. 'When the latch valve I00 has been thus moved, control fluid is communicated through the central chamber thereof with conduit I05 leading to the top of tube pawl control cylinder I04. The projectiles having already been lifted; from the tube pawls 23, they are now retracted by the downward movement of piston I03 in the manner previously indicated. It Will be noted that from conduit I05 fluid is admitted to a? chamber I00b at the right-hand end of the latch valve I00 so that it will be retained in its left position in order that fluid will continue to act on the top of piston I03 for a certain period of time after the loaded hoist bar starts its descent and the top-of-stroke valve 80 has been released by the arm 93 to return to its right extended position.

As the loaded hoist bar 20 moves downwardly, rod 93a on arm 93 releases the tube pawl control valve 95after the bottom of each projectile has passed below the tube pawl from which it was lifted. lressure acting on the piston 95a. of the tube pawl control valve 95 again shifts it to its extreme right position whereby fluid flowing from passage I25 is no longer communicated with passage I26 and the latter is vented to the expansion tank through passages I22a, I22, and the function control valve. This permits the spring I00a to move the latch valve I00 to the right, porting passage I05 to the passage communicating with the drain passage I'Ia. so that fluid above the piston I03 will be vented to the expansion tank; Passage I25 is now communicated with conduit I06 to again admit fluid to .the bottom of piston I03 to move it to its upper position to thereby extend the tube pawls 23 to projecile retaining position in readiness to receive the projectiles as the hoist bar continues .its descent.

It will be noted that with the function control valve 5I in the position of lower" no escape is providedfor excess fluid in the control circuit except through a relief valve I200 which is provided in the left-hand side of the control block '50. This relief valve is set to maintain in the 13 other forces imposed on these pistons during the process of lowering projectiles.

The stroke limit piston H operating in the tilting plate control block 80 is provided with a depending extension H511 which is adapted to engage a groove or slot 82b on the top of the tilting plate positioning piston 82 when stroke limit piston H 5 is in its down position during the lowering cycle. The slot 822) is of a ize to permit thetilting plate positioning piston 82' to be moved to its "leftmost position to allow .pump 12 to deliver full "fluid now to the lower end of the hydraulic cylinder '28 a hereinbefore described. The left end of the slot 821),. however, abuts the extension 5b of the piston H5 when the piston '82 urged to the right during the down stroke phase of a lowering cycle so that the tilting plate l3 may not be moved to its full right position. Thus, the loaded hoist bar moves down by' the force of gravity rather than by hydraulic pressure and consequently; under this condition, pump I-2 actually becomes a motor, and the electric motor in acts as a generator, to prevent the hoist bar from moving down at a speed greater than that for which the tilting plate .posltioning piston '82 is set. V

Referring to servo outlet passage Mb, itwill be noted that when the function control valve in its down position servo fluid is no longer in communication with passage b leading to the interlock valve 61. Servo fiuid is, however, ported to an upper passage 10.; leading to the interlock valve which passage is uncovered when a projectile acts on the upper interlock bell crank 61, as previously described, to move the inter- 1 look valve 61 to the left. This initiates theupstroke phase of a lowering cycle in a manner similar to the placing of projectile on the loading platform '51 to initiate the upstroke phase of a raising cycle.

It should be noted that the servocircuitis completely separate from the control circuit, the only common passageways being the drain passage conducting fluid to the expansion tank l1. Furthermore, it should be noted that all valves that completely filled with fiuid to provide a seal about the valves operating in the control block 50.

The operation of the hoist is as follows:

With no projectiles in the hoist tube, with the function control valve 51 in the position of "raise," and with the electric motor in running, all the parts of the hoist and control mechanism therefor will assume the position in the illustra tion. When a projectile is placed on the loading platform 5'! bell crank 53 will be rotated clockwise so that interldck valve 61 will be moved to the right to port fluid to the right end of the reversing valve 13 which willthereupon move to the left. Fluid acting on "the left end of the tilting plate positioning piston 82 "will be thus vented to the expansion tank H and pressure acting on the right-hand end of the piston 82 will move it to the left so that the tilting "plate 13 ism'o'ved toward the stop '24. Hydraulic pump l2 W111 ="n'ow deliver fluid to th'e bottoi'n- Of p'i'StO'n' l4 l9 and start it-movingupwardly. Af't'er slight upward movement, upper boss. 2th on the hoist bar releaseslever 9| so'that bottom-of-stroke valve 12 will be moved to the right by its spring 12b. Thi shuts off the supply of. fluid to the right end of the reversing valve 13 which is retained in its left position by its nonpositive detent 13c. ascent the lowest hoist bar pawl 21 engagesthe bottom'of the projectile and lifts it from the loading platform 51. When the bottom of the projectileghas passed above the arm- 53a of the bell crank 53 the interlock valve 61 is returned to its neutral position by the action of its spring 61b so that servo fluid can- -no longerflow' to the bottom-of-stroke valve 1-2; Fluid, however, continue to be pumped through the reversing valve 13 to the right-hand end of tilting plate positioning piston 82 so that pump [2 continues to deliver fluid to the bottom of piston 19. the hoist bar 2i) approaches the top of- 'its'strolte it is uniformly decelerated bythe buffer 33. "At this point the projectile has passed abovethe lowest tube pawl '23 and it assumes its normal position beneath the bottom of the projectile. As the bufling piston33 'nea-rs the end of its stroke, lever 91 is engaged by lower boss 21 on the hoist bar 20 to cause arm 93 to push against the top-of-stroke valve 80 to move it and the latch valve Hill to the left thus porting sum to the left end of the reversing valve. ,When this member has been moved to the right, fluid acting on the right end of the tilting plate posi-'- tioning piston 82 is vented to the expansion tank 11 and pressure is-now exerted on the left end of the tilting plate positioning piston so that it moves toward the right stop 2-3 to thus reverse the flow of fluid to the hydraulic cylinder '28. Piston I9 now commences the downstroke phase of the raising cycle.

After about the first inch of downward travel of the hoist bar 20 the top-of stroke valve '80 is released by the arm "93 so that it again assumes its rightwardly extended position and servo fluid no-longer flows to the left end of the reversing valve 13 Fluid, however, continues to flow through the reversing valve to the'left end of the tilting plate; positioning piston 82 so that fluid is pumped tothe top of the piston [9. As the hoist bar '20 descends the projectile is seated on the first tube 'pawl 23 above the loading platform 51. When the hoist bar approaches'the bottom of its stroke, upper boss 21b thereon contacts the lever 9| causing arm 92 to shift the bottom-of-stroke valve 12 to "its left position thereby admitting servo fluid to both ends "of the tilting plate positioning piston 82 which is moved to the left by the pressureacting on the differential area pro vided by the right neutral positioning piston 83, the piston 82 being stopped in its neutral positionin'gwhen' its left end abuts the extension 842) of the left neutral positioning piston 84 as here'- inbefore described. As has been indicated, control fluid acts on the tube'p'awl control piston I113, the hoist pawl control piston I09, and the tilting plate'limit piston I I5 sothat they are all retained in their upper position during all phases o'f'th raising cycle.

With no projectile on the loading platform 51 all the parts of the hoist assume the position illustrated When 'a second projectile is placed on the loading platform the hoist repeats the above-described cycle of operation, and continues to do so as longas projectiles are sups plied to the loading platform until the firstpro? As the hoistbar 20 continues its 15 jectile has reached the top and final flight in the hoist tube so that the upper interlock .bell crank BI has been rotated counterclockwise to move the interlock valve 61 to its left position.' This renders the hoist inoperative even though a new projectile has been placed on the loading platform 351. However, when the upperprojectile has been removed from the hoist tube the interlock valve will assume its rightwardlyextended position so that another raising cycle may be initiated to move all projectiles one flight, and the hoist will continue to function as long as new projectiles are placed in the bottom of the hoist tube and raised projectiles are removed from th top of the hoist tube. V

Assuming now that there are no projectiles in the hoist tube and the hoist tube is'to be operated to lower projectiles, the operator moves the lever 52 to flower" so that the function control valve is in its down position. Servo fluid now flows through the upper passageway s to the interlock valve 61 but continues to flow through the passageway 10a to the various parts of the hoist control operated by servo pressure.

. When a projectile is placed in the top of the hoist, upper interlock bell crank BI is rotated counterclockwise to move interlock valve 61 to the left and admit servo fluid through the bottom-ofstroke valve to the right end of the reversing valve13 which is moved to the left to admit fluid to the right side of the tilting plate posi tioning piston 82 and to vent fluid on the left side thereof to the expansion tank I'l. Control fluid has already been admitted to the top of the tilting plate limit piston I I5 and the tripping cam piston I09 so that they are now in their down position where they remain throughout the pro jeetile lowering cycle. The tube pawl control .valve195 is moved to the right by control pressure acting on its differential piston 95a and tube pawl control piston I03 remains temporarily in its upper position.

a As the tilting plate I3 approaches the stop 24 fluid is delivered beneath the piston I9 as before and the hoist bar starts its ascent. After approximately the first inch of ascent the bottomof-stroke valve 12 is released and moved to its right-position shutting off fluid to the right end of the reversing valve. The interlock valve 61 remains in its left position since a projectile is still seated on the uppermost position of the hoist tube biasing upper interlock bell crank GI count erclockwise as aforesaid. As the hoist bar approaches the top of its stroke the hoist bar operating lever SM is engaged by lower boss He and moved counterclockwise so that rod 9311 on arm 33 may move the tube pawl control valve 95 to the left to admit control fluid to the latch valve I00. At approximately this moment the projectiles are unseated from the tube pawls .23. When arm 93 has pushed the top-of-stroke valve 80 and the latch valve I00 to the left, control fluid is admitted to the upper side of the tube pawl control piston I03 to move-it downwardly to retract the tube pawls 23. Control fluid is also admitted to the right end of the latch valve I00 to retain it in its left position so that control fluid will continue to flow to cylinder I04 until the bottom of the projectile is below the tube pawl from which it has been lifted.

With the top-of-stroke valve 80 in its retracted .or left position servo fluid is .now admitted to the left end of the reversing valve 13 which is shifted to its righthand position so that fluid is directed to the left end of the tilting plate positioning piston 82' which is moved toward the right until the left edge of the grove 82b on the top thereof abuts the depending extension II5b of the stroke limit piston H5. The tilting plate I3 is thus stopped slightly to the right of its neutral position so that only sufficient fluid is pumped to the top of the piston l9 to prevent the formation of a partial vacuum. The weight of the loaded hoist bar, however, is sufficient to move it downwardly by the force of gravity, the fluid beneath the piston I9 acting to drive the pump .I2 as a motor so that the speed of descent will be held within the desired limit. When the arm 93 releases the top.- of-stroke valve so that it returns to its right extended position fluid will be shut off to the left end of the reversing valve 13 as aforesaid. When the bottom of the projectile is below the uppermost tube pawl 23, the rod 93a on the arm 93 moves out of contact with the tube pawl control valve 95 which is returned to its right extended position by fluid acting on its left end 35a as before described thereby shutting off control fluid supplied to the right end of the latch valve I00 and the fluid supplied to the conduit I05 leading to the top ofthe tube pawl control piston I03. The latch valve I00 is moved to the right by its spring I00a venting conduit I05 to the expansion tank I! and control fluid is once again admitted to the conduit I06 50 that the tube pawl control piston I03 may be forced upwardly to return the tube pawls 23 to a projectile retaining position so that as the bar 20 continues to descend the projectile will be lifted off its hoist pawl by the next lower tube pawl where it is retained untilthe next cycle of the hoist bar. As said bar nears the end of its down stroke the boss 2Ib engages the lever 9I so that arm 92 can shift the bottom-of-stroke valve 12 to the left whereby fluid is admitted equally to both sides of the tiltin plate position ing piston 82 as before. a v

When another projectile is placed in the top of the hoist tube the interlock valve 61 is shifted to the left so that the cycle may be repeated as described. During the upstroke, when the uppermost hoist pawl approaches the bottom of the projectile seated-onth next flight below the top, the upper tripping cam I 080 retracts the bar pawl clear of the projectile until said pawl has been raised above the bottom of the projectile. When the hoist approaches the end of its upstroke the projectiles are lifted from the tube pawls which are again retracted as described and the hoist bar completes the down stroke phase of the lowering cycle as before indicated. This operation continues as long as projectiles are placed in the top of the hoist and removed from the bottom.

Provisions are made for operating the hoist manually for drill purposes and the like. A bypass valve I30 is provided in the lower left side of the control block 50 which may be opened to port all servo fluid supplied by servo pump I4 to the expansion tank so that the servo circuit is at the same pressure.

The tilting plate I3 is engaged by a suitable pin I3b with the manual control leverl3a which is moved in one direction or the other to control the pump I2. A signal light (not shown) in series with a switch (not shown) operated by the hoist bar may be provided to indicate when the bar reaches the top of the stroke. The operator reverses the tilting plate I3 when the signal light is energized."

. Should it be desired to reverse the movement of the hoist bar after an emergency stop, the by-pass valvel30 is opened to equalize the presstroke valve responsive to said hoist bar movement upon its reaching the lower limit of its reciprocatory cycle for placing said pump control piston in neutral position, a directional control valve movable between object raising and object lowering position for establishing the direction of object movement, and means cooperating with said last named valve in object lowering position to retract said bar pawls and said guide pawls in correlation with hoist bar position to accomplish the lowering of objects in said hoist.

5. A device for moving objects between two locations by stepwise advancement of the objects through a plurality of stations comprising; a hydraulic hoist and control system for said hoist; said hoist comprising: an object advancing bar having a reciprocating cycle of operation, pawls retractedly mounted on said bar for engaging objects in said hoist, a stationary object guide cooperating with said bar, retractable pawls positioned in said guide at each station for supporting objects moved thereto by the reciprocation of said bar; said hoist control comprising: means or reciprocating said bar, a hydraulic control piston for actuating said reciprocating means, the movement of said bar being dependent upon the position of said piston, an interlock valve for rendering said hoist inoperative until an operative load condition prevails in said hoist, means responsive to said operative load condition for moving said interlock valve to hoist operation position, a reversing valve cooperating with said interlock valve for determining a first position of said control piston to move said bar upwardly, a top-of-stroke valve responsive to said hoist bar movement upon its reaching the upper limit of its reciprocatory cycle for actuating said reversing valve in opposition to the efiect of the interlock valve thereon thereby reversing said bar, and a bottom-of-stroke valve responsive to said hoist bar movement upon its reaching the lower limit of its reciprocatory cycle for placing said control piston in a nonbar operating position thereby stopping said hoist until an operative load condition again prevails in said hoist.

6. In a conveyor for moving objects between two locations by stepwise advancement of the objects through a plurality of stations, a control system therefor comprising: means for reciprocating said conveyor substantially over the span between stations, a hydraulic pump for operating said conveyor reciprocating means, a pump control means movable between a conveyor stop and two conveyor operating positions, an interlock valve for rendering said conveyor operative only under a predetermined load condition thereon, means responsive to conveyor load condition for controlling said interlock valve, a reversing valve cooperating with said interlock valve for moving said control means to oneof said two conveyor operating positions, means responsive to conrveyor movement upon its advancing objects substantially the distance between two stations for actuating said reversing valve in opposition to the effect of the interlock valve thereon for moving said control means to the second of said two conveyor operating positions to reverse said conweyor, means for supporting said objects at each station when advanced thereto by said conveyor, means responsive to said conveyor movement in its reverse direction for moving said pump control means to conveyor stop position, and a function control means for establishing the direction of object movement by said conveyor.

7. A device for moving objects from a first to a 20 second station comprising a hoist bar, a piston for reciprocating said hoist bar, means for retaining said objects at said stations, and a control system for said hoist; said control system comprising: a pump for reciprocating said bar' piston, a pump discharge control pis't'on movable between hoist operating and hoist stop positions, a circuit for conducting fluid to said second piston for actu ating the same, load operated means at said stations of said hoist for retaining said circuit closed with an object in said second station, said means being responsive to the placing of an object in the first station and the removal of an object from the second station for opening said circuit to cause said second piston to move to a hoist operating position, a top-of-stroke valve in said circuit biased to closed position, means responsive to said hoist bar movement upon reaching the upper limit of its reciprocatory cycle for opening said top-of-stroke valve to move said second piston to a position reversing said hoist bar movement, a bottom-of-stroke valve in said circuit biased to closed position, and means responsive to said hoist bar movementupon reaching the lower limit of its reciprocatory cycle for opening said bottom-of-stroke valve to cause said second piston to move to hoist stop position, and a function control valve for determining the direction of object movement.

8. A device for raising and lowering objects by stepwise advancement of the objects through a plurality of successive stations comprising a hydraulic hoist and a control means therefor; said hoist comprising an object advancing bar, pawls mounted thereon for engaging and advancing said objects, a hydraulic piston for linearly reciprocating said bar, a stationary object guide cooperating with said bar, pawls positioned on said guide at each station for supporting objects advanced thereto during bar reciprocation, means for positively retracting said bar pawls, means for positively retracting said guide pawls, the direction of object movement during operation of the hoist being determined by the operation of said guide and bar pawl retracting means; said bar pawl retracting means comprising: a piston operable between bar pawl tripping and nontripping position and biased to nontripping position; said guide pawl retracting means comprising: a piston operable between guide pawl extended and guide pawl retracted positions and biased to pawl retracted position; a circuit for conducting fluid to said last two mentioned pistons, a function control valve in said circuit movable between object lowering and object raising positions, said valve in object lowering position admitting fluid through a branch of said circuit to said bar pawl piston to replace it in pawl tripping position, a guide pawl control valve in the second branch of said circuit biased to closed position, means responsive to upward hoist bar movement for opening said guide pawl control valve, a latch valve in said second circuit biased to closed position, means responsive to hoist bar movement upon its reaching substantially the upper limit of its reciprocatory cycle for opening said latch valve thereby moving said guide pawl piston to pawl retractedposition, means for locking said latch valve in open position until closure of said guide pawl control valve, said latch and said guide pawl control valve returning to closed position upon said hoist bar lowering said object below the guide pawls theretofore supporting said objects and below the guide pawls control valve actuating position of said hoist bansaid guide pawls being extended upon closing of said valves to receive objects being lowered; said control means for said hoist comprising a pump for reciprocating said bar piston, and a pump discharge control means for determining the direction of bar piston movement; thereby providing for the raising or lowering of objects by reciprocation of said bar and the cooperation of the pawls therewith.

9. A device for moving objects between two locations by stepwise advancement of the objects through a plurality of stations comprising. a hydraulic hoist and a control system for said hoist; said hoist comprising: an object advancing bar, a reciprocable hydraulic piston on said bar, pawls retractedly mounted on said bar for engaging objects in said hoist, a stationary object guide cooperating with said bar, retractable pawls positioned in said guide at each station for supporting objects moved thereto by said bar; said hoist control system comprising, a hydraulic pump for reciprocating said hydraulic bar piston, a pump discharge control piston for determining the speed and direction of bar piston movement, an interlock valve for rendering said hoist operative only under a predetermined load condition thereon, means responsive to said operative load condition for actuating said interlock valve, a reversing valve cooperating with said interlock valve for determining the position of said control piston, a top-of-stroke valve responsive to said hoist bar movement upon its reaching the upper limit of its reciprocatory cycle for actuating said reversing valve in opposition'to the efiect of the inter lock valve thereon, and a bottom-of-stroke valve responsive to said hoist bar movement upon its reaching the lower limit of its reciprocatory cycle for placing said pump control piston in a position stopping said pump discharge thereby stopping said hoist at the end of its reciprocatory cycle.

DAVID WERTMAN. ROBERT K. BOLE.

No references cited. 

